The present invention relates generally to signal couplers, and more particularly to a radio frequency (RF) coupler apparatus suitable for use in a multi-band wireless communication device, such as a dual band wireless telephone.
A dual band wireless telephone is capable of operating in two communication systems, each characterized by a different frequency band. One existing dual band wireless telephone operates in both the Global Standard for Mobile (GSM) digital system by transmitting RF signals in a frequency band from 890 MHz to 915 MHz (xe2x80x9cGSM 900xe2x80x9d) and the GSM 1800 digital system by transmitting RF signals in a frequency band from 1710 MHz to 1785 MHz (xe2x80x9cGSM 1800xe2x80x9d). Another existing dual band wireless telephone operates in both the Advanced Mobile Phone Service (AMPS) analog system by transmitting RF signals in a frequency and from 824 MHz to 849 MHz (xe2x80x9cAMPS 800xe2x80x9d) and the 1900 MHz Time Division Multiple Access (TDMA) IS-136 digital system by transmitting RF signals in a frequency band from 1850 MHz to 1910 MHz (xe2x80x9cTDMA 1900xe2x80x9d or xe2x80x9cD-AMPS 1900xe2x80x9d).
Prior art transmitter circuitry 100 of a dual band wireless telephone is shown in FIG. 1. The transmitter circuitry 100 includes RF power amplifier 102 to amplify RF signals in a first frequency band TX BAND 1 for transmission at an antenna, and RF power amplifier 103 to amplify RF signals for transmission in a second frequency band TX BAND 2 at the antenna. To measure the power level of the transmitted RF signals, the transmitter circuitry 100 uses a RF coupler apparatus 104 with two separate transmission line coupling structures 106 and 107, which are coupled in parallel at a summing junction 108 via respective detection diodes 110 and 111 of a RF power detector 109. Each of the coupling structures 106 and 107 have a coupler (i.e., couplers 112 and 113) and a termination device (i.e., termination devices 114 and 115). The RF power detector 109 outputs a RF detect signal, which has an amplitude related to the amplitude of the RF signals output by RF power amplifier 102 or 103. The RF detect signal is used to control the power level at which the dual band wireless telephone transmits.
The RF coupler apparatus 104 requires that the RF power detector 109 include one detection diode per coupling structure. It can be appreciated that when the dual band wireless telephone is portable or hand-held, an important goal is to minimize component count. Modifying the RF power detector 109 by moving the summing junction 108 to the input of the RF power detector 109 (i.e., to the anode of detection diode 110) and removing the detection diode 111 would result in an unacceptable RF voltage loss at the input of the RF power detector 109 and a reduction in the sensitivity of the RF power detector 109. Therefore, what is needed is a RF coupler apparatus that is suitable for use in a multi-band wireless communication device and reduces duplication of components in an RF power detector.